The Influence of Grape Rootstocks on the Crown Gall Infection Process and on Tumor Development

¹ Department of Plant Pathology, University of Missouri, Columbia, MO 65211,
² Research Scientist and Technician, respectively, Eidgenossische Forschungsanstalt for Obst, Wein und Gartenbau, Wädenswil, Switzerland.

Stem tissue explants from greenhouse grown-rootstock, 5C, SO4, 5BB, 8B, and 125AA were inoculated with Agrobacterium tumefaciens. Rootstock 5C was, by far, the most tumorigenic. Twenty-five clones of the five rootstocks and of rootstock 3309C from nurseries in Switzerland, Germany, and Italy were examined for the presence of A. tumefaciens in their vascular fluids. The greatest number rootstock pieces containing virulent populations of the pathogen was 5C. The formation of large, soft, and friable callus at the base of grafted 5C rootstock pieces during the heat-callusing process appears to provide ideal sites of penetration by the pathogen and the opportunity for transformation of grape cells and subsequent tumor development. The data suggest that 5C is an inordinately sensitive host to A. tumefaciens. As a consequence, its use in replanting vineyard sites where spring frosts are likely is hazardous.

Key words: Agrobacterium tumefaciens, crown gall, rootstock

Submitted on December 26, 1991